This invention relates to the field of gas turbines, and more particularly to methods and apparatus for cooling
In order to cool their hot parts, in particular the combustor and the turbine through which the hot gas flows, existing gas turbines (gas turbine systems) use either cooling media taken from the compressor at a suitable pressure-and which sometimes are further cooled-and which, after they have been used to cool the hot parts, are added to the turbine stream; or these existing gas turbines use closed cooling circuits supplied from an external cooling medium source, in most cases water or steam. Such a method and such a gas turbine system are known, for example, from publication U.S. Pat. No. 5,611,197. In the latter case, frequently found in combination power plants, the cooling heat often can be used in the process that follows. Another possibility, described, for example, in EP-A2-0 899 425 of the applicant, combines, especially in the case of blade cooling, a closed steam cooling system in the main part of the blade with an open cooling system in the area of the leading blade edge.
The first category has the disadvantage that the cooling medium, which inherently bypasses heating in the combustor, in most cases undergoes a higher pressure loss in the cooling section than is necessary for the cooling task. In addition, mixing losses are created when the cooling medium enters the main stream. Both represent significant process losses that have an important adverse effect on the efficiency of the process overall.
The second category of externally supplied cooling systems and, in particular, also the third category of the combined cooling systems, does not have these disadvantages or is only affected by them to a limited degree; however, their operation becomes dependent on an external coolant supply, which is associated with an increased level of complexity as well as increased cost and safety risks.
The initially mentioned U.S. Pat. No. 5,611,197 discloses a gas turbine with a closed cooling system for the guide and rotating blades and the hot gas housing of the turbine, in which air with a specific pressure is removed from the compressor at an intermediate pressure level or at the outlet, this air is supplied as cooling air through the components to be cooled, and is then again fed into the compressor at a suitable, lower pressure level. Prior to being fed into the compressor, the returned cooling air hereby also can be additionally cooled inside a cooler.
This known type of closed cooling circuit has significant advantages in terms of simplicity of design and operation and influence on the overall efficiency when compared to the types of cooling described previously in this document. The disadvantage is, however, that in the case of a recooling of the cooling air, external cooling media (52 in the figure of U.S. Pat. No. 5,611,197) are used to cool down the returned cooling air in a heat exchanger (50). The heat removed in the heat exchanger in this way is removed in an efficiency-reducing manner from the process of the gas turbine system and at most can be utilized with additional expenditure.
It is therefore the objective of the invention to disclose a cooling method for a gas turbine as well as a gas turbine system for performing said method that avoids the disadvantages of known methods of gas turbine systems and is characterized, in particular, by a simple and substantially efficiency-neutral recooling.
The concept of the invention is to perform at least a substantial part of the recooling with at least one part of the compressor end air as a cooling medium. The heat removed from the cooling air in this way is easily returned into the process of the gas turbine system. The recooling of the cooling air with the compressor end air is hereby preferably performed in a heat exchanger, in particular, in a counter-current heat exchanger.
According to a first preferred embodiment of the method according to the invention, the cooling air is passed in a completely closed cooling circuit through the components to be cooled. This ensures that no compressed air passes by the combustor in an efficiency-reducing manner and reaches the main stream.
A second preferred embodiment is characterized in that a part of the cooling air is fed for film cooling through drilled film cooling openings on the components, in the manner of a targeted leakage, into the turbine stream. This makes it possible to achieve a very effective additional film cooling of the exterior surfaces of the components to be cooled with only slight losses of compressed air.
The thermally loaded components cooled with the cooling air preferably include the walls of the transition areas combustor/gas turbine and/or housing parts of the turbine and/or rotor parts of the turbine and/or blades of the turbine. If the blades of the turbine are cooled with cooling air, it is particularly effective if drilled film cooling openings are provided on the leading blade edges and/or the trailing blade edges.
If a pressure loss occurs in the cooling air during the cooling process, the cooling air must be recompressed after the cooling process. It is preferred that the compressor of the gas turbine system itself is used to recompress the cooling air after the cooling process, or an external compressor is used.
If the recooling in the heat exchanger with the compressor end air is insufficient, a further aftercooling of the cooling air is performed after the recooling with the compressor end air, for which preferably a cooler through which a separate cooling medium flows is used. However, it would also be conceivable and reasonable to inject water directly into the cooling air in order to aftercool the cooling air.
A preferred embodiment of the gas turbine system according to the invention has second cooling lines that merge into the compressor at an intermediate pressure level. It would also be conceivable, however, that instead of this, an external compressor is located in the second cooling lines, and that the second cooling lines merge into the outlet of the compressor of the gas turbine system.